GB634777A - Improved manufacture of amino-aldehyde adhesives - Google Patents

Abstract

A process of making an aqueous adhesive extended with wheat flour and having a pH between 2.5 and 6 comprises mixing wheat-flour with a urea- and/or melamine-formaldehyde condensation product, or the reactive constituents from which the condensation product is later to be formed when the adhesive is to be used and a water-soluble bisulphite in a concentration of 1-6 per cent based on the wheat flour. About 50-250 parts of flour to 100 parts of condensation product may be used. The bisulphite may be added at any stage before addition of water, and excess is not objectionable. Catalysts, buffering agents, hardeners and accelerators, and modifiers such as thiourea, phenol, resorcinol, soluble blood albumen and the like (as such, or as resinous condensation products with aldehydes or coreacted with the amino-aldehyde resin) may be added. The adhesive may be used in hot or cold press methods, in the latter case with the addition of acid catalysts preferably after mixing the flour, bisulphite, and water. In examples: (I) spray dried urea-formaldehyde adhesive resin, sodium bisulphite, flour, and water were mixed in a glue mixer to form an adhesive of pH 4.5. (II) An aqueous composition of finely ground dimethylol urea, flour, sodium bisulphite, oxalic acid and water was mixed to form an adhesive of pH 5.1. Alternatively, the dimethylol urea is dissolved in part of the water at 180 DEG F. and the other ingredients then added, followed by cooling to precipitate fine particles of dimethylol urea. A further method is to use coarse dimethylol urea in the mixture which is then made smooth by passage through a gear pump. (III) An adhesive of pH 4.2 for hot pressing comprises a mixture of urea, formalin, flour, sodium bisulphite, oxalic acid, and water. (IV) Dry powdered melamine/formaldehyde adhesive resin, sodium bisulphite, flour and water is mixed to form an adhesive of pH 5.5, better results being obtained at pH 5.5. (V) An adhesive of pH 5.5 or 4.2 comprises a mixture of finely ground melamine, formalin, flour, sodium bisulphite, oxalic acid, and water. (VI) Urea, melamine, formalin, flour, sodium bisulphite, oxalic acid and water are mixed to form an adhesive of pH 5.5 or 4.2. The melamine of the examples may be substituted by up to 25 per cent of blood albumen. The compositions may be prepared as mixtures containing the resin with flour or formalin, formalin or flour, as the case may be, being added by the user to complete the process. The Specification as open to inspection under Sect. 91 states that the condensation product may be modified with furfural and acetaldehyde. This subject-matter does not appear in the Specification as accepted.